Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.6.3.44 (P-glycoprotein)
13,344 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Natural killer (NK) cells have been reported recently to be the highest in expressing multidrug resistance (MDR) P-glycoprotein among normal mature lymphoid cells. Using a cultured NK cell-rich population, we have examined the expression and function of P-glycoprotein, in particular its role in NK cell-mediated cytotoxicity, by employing two MDR-reversing agents (nicardipine and AHC-52, a nicardipine analog almost devoid of calcium channel blocking activity) and monoclonal antibody against P-glycoprotein (MRK-16). The expression of P-glycoprotein was detected by flow cytometry and polymerase chain reaction of reverse transcribed mRNA. P-glycoprotein was functional in terms of rhodamine dye excretion and its susceptibility to the MDR-reversing agents. Since the concentration of nicardipine required for 50% inhibition (IC50) of rhodamine dye excretion (2 microM) was close to that of AHC-52 (5 microM), it was suggested that their inhibitory effects were not due to calcium channel blocking activity, and that ACH-52 is a selective inhibitor for P-glycoprotein. The IC50 of nicardipine for NK cell-mediated cytotoxicity (33 microM) was also close to that of AHC-52 (26 microM), indicating that P-glycoprotein is involved in NK cell-mediated cytotoxicity. In support of this, MRK16 inhibited NK cell-mediated cytotoxicity in a concentration-dependent manner. Both binding of target cells to NK cells and post-binding events were affected by AHC-52, suggesting that P-glycoprotein is involved in several steps in NK cell-mediated cytotoxicity.
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PMID:Expression and function of multidrug resistance P-glycoprotein in a cultured natural killer cell-rich population revealed by MRK16 monoclonal antibody and AHC-52. 798 Jun 29

The surface and intracellular expression of mdrI-P-glycoprotein in parental drug-sensitive human breast cancer cells (MCF-7) and their multidrug-resistant (MDR) variants has been studied by using the monoclonal antibodies (MAbs) MM4.17 and MRK-16, which recognize 2 different epitopes of the drug efflux pump molecule. Fluorescence microscopic observations showed that P-glycoprotein, in addition to being located at the cell surface, can also be found in the Golgi apparatus of resistant cells. To confirm this finding, Golgi apparatus and P-glycoprotein were double-labelled with wheat-germ agglutinin (WGA) and MAb MM4.17. Laser scanning confocal microscopy indicated that, in MDR cells, Adriamycin mainly accumulated cytoplasmically in a perinuclear region. This accumulation proved to be modulated by pre-treatment with verapamil or ATP depletion. Moreover, the vital staining of Adriamycin-treated MDR cells, performed with the fluorescent lipid N-[7-(4-nitrobenzo-2-oxa-1,3-diazole)]- 6-aminocaproyl sphingosine (C6-NBD-ceramide), revealed that the anthracyclinic antibiotic was located in the Golgi apparatus. All these results indicate that the drug transporter is located in the Golgi apparatus, in which Adriamycin molecules also accumulate.
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PMID:P-glycoprotein expression in the Golgi apparatus of multidrug-resistant cells. 798 20

In order to clarify the mechanism of drug resistance in human myeloma cells, we investigated the expressions of DNA topoisomerase I and topoisomerase II gene and the genes possibly related to drug resistance; multi-drug resistant gene 1 (MDR-1), glutathione S-transferase class pi gene (GST-pi), by Northern blotting. Myeloma cells in eight of 15 cases prior to chemotherapy expressed topoisomerase I mRNA considerably, while the expression of topoisomerase II mRNA was detected weakly in only one of 16 myeloma patients. There was not any correlation between expression of topoisomerase I mRNA and clinical drug resistance. Significant expression of MDR-1 mRNA and P-glycoprotein was not detected in 25 cases of multiple myeloma prior to chemotherapy and even after several courses of VAD (vincristine, adriamycin and dexamethasone) therapy by Northern blotting and immunostaining using monoclonal anti-P-glycoprotein antibody (MRK-16), respectively. On the other hand, 16 of 21 myeloma cases showed significant expression of GST-pi protein and GST-pi mRNA with the various strengths, but there was no apparent correlation between GST-pi mRNA expression and clinical response. Therefore these data suggest that expression of the genes we tested may not determine the level of drug resistance in multiple myeloma, but lower or no significant expression of topoisomerase II mRNA in most myeloma cells indicates the possibility that topoisomerase II inhibitors such as VP-16 and topoisomerase II-mediated cytotoxic drugs such as adriamycin, are not so effective for the treatment of multiple myeloma.
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PMID:Expressions of DNA topoisomerase I and II gene and the genes possibly related to drug resistance in human myeloma cells. 809 26

A rapid and simple functional assay for P-glycoprotein (Pgp) using flow cytometry to measure the accumulation of the flurophore fluo-3 has been applied to samples from patients with B-cell chronic lymphocytic leukaemia (B-CLL). Peripheral blood lymphocytes from 37 patients with B-CLL were studied for Pgp. Pgp expression, using MRK-16, a monoclonal antibody recognising an external surface epitope of Pgp, was detected in 92% of patients with B-CLL. The functional assays for Pgp expression were positive in 78 and 59% of patients using the fluo-3 and doxorubicin (dox) assays, respectively. When compared with the MRK-16 assay, the fluo-3 assay had a sensitivity of 82% compared to a sensitivity of 56% for the dox assay (P = 0.004). The specificity of the fluo-3 and dox assays could not be evaluated because of the low number of MRK-16 negative CLL cells.
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PMID:Clinical application of a rapid, functional assay for multidrug resistance based on accumulation of the fluorescent dye, fluo-3. 809 47

The synergistic effect of MRK-16, a monoclonal antibody against P-glycoprotein, and cyclosporin A (CsA) on the modulation of vincristine resistance was studied by isobologram analysis in three different, highly multidrug-resistant tumor cells. In all cell lines, the synergistic effect was demonstrated at various concentrations of MRK-16 and CsA. While MRK-16 alone did not enhance the sensitivity of the moderately resistant KB-8-5 cells to vincristine, it increased two-fold the reversing effect of cyclosporin A at 1 microM, an achievable blood concentration. Since MRK-16 alone showed therapeutic effects against multidrug-resistant tumors, the combined use of MRK-16, CsA and antitumor agents should provide therapeutic benefits for the treatment of resistant tumors.
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PMID:Enhancement of reversing effect of cyclosporin A on vincristine resistance by anti-P-glycoprotein monoclonal antibody MRK-16. 810 May 62

Anthracyclines and etoposide have been implicated in the multi-drug resistance phenotype. The mdr 1 gene encodes for the transmembrane protein P-glycoprotein. P-glycoprotein expression was measured in the fresh blast cells from 19 patients with acute myeloid leukemia using three monoclonal antibodies, C219, JSB-1 and MRK 16, and immunocytochemistry with the enzyme alkaline phosphatase as marker. Drug resistance can be identified in vitro using the predictive chemosensitivity test, the MTT (3-4,5-dimethylthiazol-2,5-diphenyl tetrazolium bromide) assay. In order to assess cell viability after drug exposure, this technique utilises the ability of cellular dehydrogenase enzymes to reduce the tetrazolium salt MTT to formazan. In vitro resistance to multi-drug resistance related cytotoxic agents was identified in the blast cells from these patients. This study showed no correlation between the results of the MTT assay and P-glycoprotein expression in this disease, suggesting either that more sensitive techniques are required to measure P-glycoprotein expression or that other drug resistance mechanisms may be involved.
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PMID:Comparison of P-glycoprotein expression with in vitro drug sensitivity in fresh blast cells from acute myeloid leukaemia patients. 852 96

The MCF-7 doxorubicin-resistant cell line MCF-7/Dox has been used extensively for studies of the multidrug resistance phenomenon. Using fluorescence-activated cell sorting (FACS), these cells were separated into two populations on the basis of rhodamine 123 (R123) accumulation. We designated these as low P-glycoprotein (LP-gp) and high P-gp (HP-gp) cells on the basis of their P-gp content. Using the reverse transcriptase polymerase chain reaction technique controlled by homologous internal standards, we analysed levels of MDR1 and MDR2 mRNA in each cell type. LP-gp and HP-gp cells had MDR1 mRNA levels of 2.17 +/- 0.17 and 6.65 +/- 2.29 amol ng-1 total RNA respectively, compared with 0.00088 +/- 0.00005 amol ng-1 in wild-type MCF-7 cells (MCF-7/WT). MCF-7/WT cells additionally contained 0.023 +/- 0.016 amol ng-1 of MDR2 mRNA, which was unchanged in LP-gp cells, but lower than in HP-gp cells, which contained 0.42 +/- 0.08 amol ng-1. Both LP-gp and HP-gp cells contained increased copies of the MDR1 gene. However, the degree of gene amplification did not correlate with the changes in MDR1 mRNA levels, indicating further regulatory levels of gene expression. The level of P-gp detected by MRK 16 correlated with R123 accumulation. HP-gp cells expressed a 10-fold higher level of P-gp1 than LP-gp cells. However, there was only a 3-fold increase in MDR1 mRNA level in HP-gp cells compared with LP-gp cells. These data suggest that some regulation of P-gp1 expression also occurred at the post-translational level. Phosphorylation of P-gp by protein kinase C (PKC)-alpha is necessary for its activity. Our analysis of PKC-alpha, 0 and epsilon isozyme levels, and subcellular distribution, shows a co-regulation of expression with P-gp, suggesting a necessary role for PKC in P-gp regulation.
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PMID:Regulation of P-glycoprotein 1 and 2 gene expression and protein activity in two MCF-7/Dox cell line subclones. 856 35

Expression of the multidrug resistance (MDR-1) gene product, P-glycoprotein (P-170), and the stem cell antigen, CD34, at diagnosis were determined using monoclonal antibodies (MoAbs) MRK-16 and 12.8 respectively, in 130 pediatric acute myeloid leukemia (AML) patients entered onto Childrens Cancer Group (CCG) study CCG-2891. Fluorescein isothiocyanate (FITC) as a second step reagent was employed for the measurement of P-170 expression since it is commonly used in clinical laboratories. Nine of 30 (30%) infant ( < 1 year of age) de novo specimens expressed P-170 at levels > or = 20% of control cells. In contrast, eight of 100 (8%) AML samples from older children ( > or = 1 year of age) expressed the multidrug resistance surface protein at diagnosis. With the exception of one infant, all de novo samples that expressed P-170 also expressed CD34. Pediatric patients of any age with positive P-170 expression using MoAb MRK-16 with a FITC-conjugated second step reagent fared no worse than remaining patients treated on the same treatment with regard to induction failure, incidence of relapse, event-free survival, or overall survival. Further investigation is necessary to determine whether P-170 assay systems with greater sensitivity will distinguish pediatric AML patients with poor prognosis.
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PMID:Cell surface expression of the multidrug resistance P-glycoprotein (P-170) as detected by monoclonal antibody MRK-16 in pediatric acute myeloid leukemia fails to define a poor prognostic group: a report from the Childrens Cancer Group. 860 15

To date, all reported measurements of multidrug resistance have been semiquantitative. The purpose of the present study is to establish and validate the self-competitive binding assay technique utilizing monoclonal antibody for quantitative estimation of multidrug resistance in tumor cells. This technique is used for P-glycoprotein concentration measurement in BE(2)-C human neuroblastoma cell line and its sublines with primary resistance to colchicine and actinomycin D. Monoclonal antibody MRK-16 was used in this study. It was labeled with iodine-125 (125I) to trace the concentration of antibody-antigen complexes. The binding data were obtained by varying the concentration of the unlabeled antibody. The results were fitted to a model equation to estimate the number of binding sites and antibody-antigen dissociation constant. The P-glycoprotein concentration was significantly higher in the resistant sublines than in the sensitive line. The highest levels were achieved in actinomycin D-resistant cells: 2.1 x 10(6) binding sites/cell versus 5.4 x 10(4) binding sites/cell in the sensitive cells. The consistency of the results was verified by repeating the study three times for each cell line. The binding assay results were confirmed by Western blot experiments performed on the same cell lines.
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PMID:Measurement of P-glycoprotein expression in multidrug-resistant human neuroblastoma cell lines using self-competitive binding assay. 866 May 14

SDZ PSC833 (PSC833), an analogue of cyclosporines, is one of the most potent modulators of multi-drug resistance (MDR). We previously reported that MRK-16, an anti-P-glycoprotein MAb, enhanced MDR reversal activity of cyclosporin A (CsA) through inhibition of P-glycoprotein-mediated CsA transport. We have examined here whether MRK-16 can enhance MDR reversal activity of PSC833. We found that MRK-16 potentiated the MDR reversal activity of PSC833, and of CsA, in MDR sublines of human myelocytic leukemia K562 and human ovarian cancer A2780 cells. Like MRK-16 combined with CsA, MRK-16 enhanced the effect of a sub-optimum dose of PSC833 on vincristine accumulation in MDR cells. However, MRK-16 could not increase cellular accumulation of PSC833 in MDR tumor cells, yet it could increase cellular accumulation of CsA. P-glycoprotein could not transport PSC833 but could transport CsA. Our results indicate that MRK-16 potentiates the MDR reversal activity of both PSC833 and CsA, yet also suggest that the molecular mechanism of the potentiation differs between the two substances.
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PMID:Potentiation of the reversal activity of SDZ PSC833 on multi-drug resistance by an anti-P-glycoprotein monoclonal antibody MRK-16. 870 21


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